This invention relates to apparatus for bending a straight tube into a serpentine tube.
As is well known, a serpentine tube used in electrical equipment is generally produced by working a straight tube 1 to form straight portions 2 and bent portions 3 therein, as shown in FIG. 1.
One type of apparatus for producing a serpentine tube of the prior art comprises a semicircular die 4 and a wing 5, as shown in FIGS. 2 to 4. In operation, a portion of the straight tube 1 to be formed into a bent portion is held between the semicircular die 4 and the wing 5, and the wing 5 is moved in rotary motion along the circumference of a circle concentric with the semicircular die 4 for an extent on the order of 180 degrees as indicated by a dash-and-dot line in FIG. 2, to form a first bent portion 3a. Then, the straight tube 1 is moved axially thereof (in the direction of an arrow in FIG. 3) for a distance L corresponding to the length of the straight portions 2. Thereafter, the straight tube 1 is moved a distance corresponding to twice the radius R of the bend of the bent portion in a direction perpendicular to the length of the straight tube 1 to hold, as shown in FIG. 3, between the die 4 and the wing 5, a portion of the straight tube 1 to be bent. The wing 5 is moved in rotary motion along the circumference of a circle concentric with the semicircular die 4 for an extent on the order of 180 degrees as indicated by a dash-and-dot line to form a second bent portion 3b. This operation is repeated to form a desired number of bent portions 3, to produce a serpentine tube.
The apparatus for producing a serpentine tube of the prior art described hereinabove has had the disadvantage that the production of a serpentine tube is a time-consuming operation and high in operating cost because the bent portions 3 are successively formed and a large number of working steps should be followed when the number of bent portions 3 is large, thereby making it impossible to provide a serpentine tube of low cost for use in heat exchangers, etc.
In order to obviate the disadvantage of the prior art, proposals have been made to use a link mechanism in apparatus for producing a serpentine tube. However, the use of a link mechanism has a serious disadvantage in that, since the spacing between bending heads is constant at all times during the operation, excess material is consumed in bending a straight tube, with a result that buckling is caused to occur in the bent portions.